Reactive Ion Etching 

Reactive ion etching is the most common form of plasma etching where ions are accelerated by the negative DC self-bias potential developed in a capacitively coupled plasma reactor. The energetic ion bombardment on the substrate sitting on the powered electrode enables anisotropic etching.

The figure below shows a schematic of a commercial tool Oxford instruments Plasmalab System 100 which is a capacitively coupled (parallel plate) plasma, CCP, excited with 13.56 MHz rf power. The plasma system was geometrically asymmetric and the plasma was confined laterally between the electrodes and extends out in the radial direction towards the outer walls. The grounded electrode also served as the shower-head to supply the feedstock gas, the chamber walls (radial) are grounded.

Figure 1 Reactive ion etcher setup from Oxford Instruments called Plasmalab system 100 (DOI: https://doi.org/10.1088/1361-6595/aa6c90)

Advanced versions of RIE are also available to achieve fast etching rate (i.e. magnetic enhanced reactive etching) and independent control of ion energies (i.e. dual frequency operated plasma reactor). Compared to conventional plasma etching, by adjusting pulse frequency and duty cycle, RF pulsed plasma etching can control the plasma properties such as ion/electron density, plasma dissociation, electron temperature, etc. and it can vary etch characteristics such as selectivity, etch profile and plasma induced damage on wafer.

Figure 2 Schematic diagram of a dual frequency CCP system. (DOI:https://spl.skku.ac.kr/_res/pnpl/etc/2020_7.pdf)